There is increasing and compelling evidence indicating that pyridoxal 5' -phosphate (PLP), the coenzymatically active form of vitamin B6, may be involved in regulating the properties of steriod-receptor complexes so as to influence steriod-receptor complex-mediated activiation of transcription. Thus, one can infer a role for PLP in the regulation of gene expression. At this point in time, nothing is known about the role(s) of PLP in the nucleus which has been reported to contain a significant fraction of total cellular PLP. This project is concerned with determining the subcellular distribution of the six B6 vitamer forms as a function of the cell cycle. Synchronilzed, hepatoma-derived cells will be incubated with radioactive pyridoxine. The distribution of pyridoxine-derived B6 vitamers in subcellular fractions obtained from synchronized cells will be determined by ion-exchange chromatography. The effects of steriod hormones (e.g., dexamethasone) known to induce the cell cycle-dependent synthesis of PLP-dependent enzymes (e.g., tyrosine aminotransferase) will be studied. Of particular interest is the cell cycle dependency of the amount of PLP in the nucleus and whether there are specific, cell cycle-dependent chromatin- associated nuclear PLP-binding proteins. These studies will provide information on the possibility of the involvement of PLP in the regulation of gene expression.